Differential effects of low concentrations of aluminium on the growth of four genotypes of white clover

Summary The effects of aluminium (Al³⁺) on the growth of four cultivars of white clover dependent upon NO₃ ⁻−N were examined. Plants were grown in flowing solution culture with carefully maintained low concentrations (0, 12.5, 25 and 50 mmolm⁻³) of Al, and with P and pH (4.5) also held constant and appropriately low. A three-week treatment period resulted in major effects on the growth and elemental composition of shoots and roots at all concentrations of added Al. There were inherent differences between the cultivars in growth but the relative effects of Al were similar in each case. Examination by S.E.M. and x-ray microanalysis of one cultivar grown at 50 mmolm⁻³ Al, indicated that Al in the roots was associated with P, especially in old, outer epidermal cells. Aluminium reduced NO₃ ⁻ uptake and there were significant effects of Al on nitrate reductase activity (NRA). In contrast to the other characteristics, there were differential effects between the cultivars in NRA, both in the presence and absence of Al.